Preliminary observation of nonlinear effects in Compton scattering

摘要

In a new experiment at the Final Focus Test Beam at SLAC a low- emittance 46.6 GeV electron beam is brought into collision with terawatt pulses from a 1.06 (mu) wavelength Nd:glass laser. Peak laser intensities of 10(sup 18) W/cm(sup 2) have been achieved corresponding to a value of 0.6 for the parameter (eta) = (ital eE/mw(sub 0)c), and to a value of 0.3 for the parameter (Upsilon) = (ital E(sup *)/E(sub crit)) = 2(gamma)(ital ehE)/(ital m)(sup 2)(ital c)(sup 3) in the case of frequency doubled laser pulses. In these circumstances an electron that crosses the center of the laser pulse has near unit interaction probability. Signals are presented for multiphoton Compton scattering in which up to 4 laser photons interact with an electron. High energy backscattered photons of GeV energy can interact within the laser focus to create electron- positron pairs; an excess of 15 positrons above a background of 14 was observed in a run of 6,000 laser shots.